Overview and development of variable frequency AC generators for more electric aircraft generation system

With the development of more electric aircraft (MEA), higher demands for electrical energy are put forward in generation systems. Compared to constant frequency AC (CFAC) generation systems, the constant speed drive (CSD) is eliminated and integrated starter/generator (SG) can be realized in variable frequency AC (VFAC) generation systems. In this paper, an overview of VFAC generators for safety-critical aircraft applications is presented, with a particular focus on the key features and requirements of candidate generators and the starting control strategies. Wound rotor synchronous machines (WRSMs) are typical generators used in VFAC generation systems so far. Meanwhile, hybrid excitation synchronous machines (HESMs) and cage-type induction machines are promising candidates for VFAC generation systems. The generation operation of WRSM is relatively mature, however, the SG technology of WRSM is still full of challenges. As one of the most important issues, the starting excitation methods of WRSM are summarized. An HESM-based VFAC SG system is proposed and developed in this paper. The experimental results show that the starting mode, transition mode and generating mode of the VFAC SG system are realized. The continuous progress of VFAC generation system makes great contributions to the realization of MEA.